1. Field of the Invention
The present invention relates to a two-piece type oil ring assembly fitted in an oil ring groove which is formed in a peripheral side of a piston for the control of lubricating oil in an internal combustion engine.
2. Description of the Prior Art
In general, an oil ring assembly for the control of lubricating oil in an internal combustion engine is of a type having a spacer expander and a pair of side rails, as illustrated in JP B 33-10104 corresponding to U.S. Pat. No. 2,789,872. The three-piece type oil ring assembly has many disadvantages one of which is that three pieces is too much in number to be assembled without introducing a mistake into the assembly. Each of the upper and lower side rails is required to move independently from the other and tightly follow the inner surface of an engine cylinder. When, upon the inclination of the piston, one of the upper and lower side rails strongly pushes a part of the spacer expander inwardly, the spacer expander is displaced inwardly to permit the separation of the outer end of the other side rail from the inner surface of the cylinder, resulting in another disadvantage in that the reduction in the oil scraping effect causes a problem of excessive oil consumption. Recently, there is the desire that he engine for use in vehicles has a reduced weight. This leads to the requirement that the piston, as well as the oil ring assembly, should be axially shorter than usual However, it is impossible to effectively shorten the axial length of the three-piece oil ring assembly.
There are disclosed two-piece type oil ring assemblies: each consisting of a single spacer expander and a single side rail shown in JP A 52-122713 corresponding to DE P 2615010.7 and JP U 55-41502. The oil ring assembly as shown in JP A 52-122713 comprises a spacer expander having a U-shaped radial section of which the axial length is similar to that of the aforementioned three-piece type oil assembly The sectional U-shaped spacer expander, made of a thin steel strip, has an insufficient force to support the inner periphery of the side rail with the result that it is easily affected by the inclination of the piston permitting the separation of the side rail from the cylinder wall. This leads to a reduction of the oil scraping effect The oil ring assembly as shown in JP U 55-41502 comprises a spacer expander having a radially crescent bottom which is unstably seated on the lower side of the oil ring groove The unsteadiness of the spacer expander results in the disadvantages that the sealing of the lower side of the oil groove is unreliable and that the spacer expander is easily affected by the inclination of the piston to permit the separation of the side rail from the cylinder wall